This invention generally relates to a multi-layer ceramic capacitor, and particularly relates to multi-layer ceramic capacitors having large capacitance.
Recently, multi-layer ceramic capacitors have been widely used to meet the need for small-sized and large-capacitance capacitors. Conventional electrolytic capacitors generally have a large capacitance, but can not operate normally at high frequencies. The multi-layer ceramic capacitors also have large capacitances and can operate normally at high frequencies. Therefore, increasing capacitance and miniaturization have become strongly desired.
Increasing capacitance and miniaturization is attained by increasing the number of the electrode layers and decreasing the thickness of the dielectric layers, in conjunction with intensive development of high dielectric constant materials. However, increasing the number of electrode layers causes increased internal stress in a multi-layered structure, so that cracks through dielectric layers or delaminations at the electrode-dielectric interfaces tend to be generated. Moreover, increasing the number of electrode layers results in increased cost of the internal electrode materials per chip.
The proposed multi-layer ceramic capacitors and related matters concerning the above-mentioned problems are classified into three groups. The first group concerns the multi-layered structure or processing method decreasing internal stress. The second group concerns dielectric materials with a high dielectric constant. The third group concerns electrode materials with low cost.
Japanese Patent Laid-Open No. 55-83216 discloses a multi-layer ceramic capacitor which uses an internal electrode containing a dielectric ceramic powder. In the sintered body, the ceramic powder dispersed at the electrode-dielectric interface behaves as an anchor. This relates to the above-mentioned first group.
U.S. Pat. No. 4,265,668 discloses high dielectric constant materials based on Pb complex perovskite oxide. These have a high dielectric constant of up to 20000. This relates to the above-mentioned second group.
U.S. Pat. No. 4,752,858 discloses a multi-layer ceramic capacitor which uses copper as an internal electrode material. This relates to the above-mentioned third group.
In the known multi-layer ceramic capacitors, electrode materials must be sintered with dielectric ceramics, so the thickness of internal electrode materials was up to 2 micrometers. If the printed electrode mass was under 2 micrometers thickness equivalent mass, the electrode layers were divided into individual parts, so the electrical connection of the electrode layers disappeared and capacity of the multi-layer ceramic capacitor was decreased.